Problem with using Autocomplete plugin

Problem with using Autocomplete plugin

I am trying to use the Autocomplete plugin and could not get it to work.

I downloaded the plugin files and included them in my aspx page as follows:
1. <link rel="Stylesheet" type="text/css" href="jQuery/jquery.ui.autocomplete.css" /> and
   <script type="text/javascript" src="jQuery/jquery.ui.autocomplete.js"></script> in the head.
2. And the following function from the Autocomplete example:

    $(function() {
        var availableTags = [
"ActionScript",
"AppleScript",
"Asp",
"BASIC",
"C",
"C++",
"Clojure",
"COBOL",
"ColdFusion",
"Erlang",
"Fortran",
"Groovy",
"Haskell",
"Java",
"JavaScript",
"Lisp",
"Perl",
"PHP",
"Python",
"Ruby",
"Scala",
"Scheme"
];
$( "#txtCreateEventByDesc" ).autocomplete({
source: availableTags
});
});
3. It gives me error on the .autocomplete call saying object doesn't support this property or method.
What Am I doing wrong?
4. If we can get it to work, how can I use a .NET page (aspx) as datasource instead of the php's in the Autocomplete example? Like:
                $("#txtCreateEventByDesc").autocomplete({
source: "db.aspx",
minLength: 2,
select: function( event, ui ) {
log( ui.item ?
"Selected: " + ui.item.value + " aka " + ui.item.id :
"Nothing selected, input was " + this.value );
}
});
In the Autocomplete example(  http://jqueryui.com/demos/autocomplete/#remote ), the file used is a php - search.php.
So basically I want to know how the page should return the data.

Thanks